It is common to lower tools and equipment (abbreviated to tools thereafter) into a borehole of a well. Such downhole tools are lowered into the borehole using a line that extends down the borehole. The term ‘line’ is intended to refer to all suitable types of line that are used in the well, such as slickline (a term commonly used in the oil and gas industry to refer to single-strand wire or braided lines) and wireline (a term commonly used in the oil and gas industry to refer to multi-strand wire or cable having electrical wires therein). The invention can be used in oil and gas wells along with other types of well. Thus the term ‘line’ is intended therefore to cover other suitable forms of line. Further the term ‘downhole tool’ is intended to refer to those tools used in the oil and gas industry, but it is also intended to refer to those that are suitable for use in other industries which employ tools used down a well on a suitable line.
Downhole tools are lowered on and/or run on a line (such as slickline or wireline) and can become stuck for various reasons. For example, a kick to the tool during perforating a well casing can cause the line or the tool to become snarled. If the tool cannot be freed a decision is often made to cut the line for abandonment or later attempted retrieval of the stuck tool. However it is desirable to cut the line below a sub-surface safety valve and preferably as close to the stuck tool as is possible. One reason for this is to ensure the subsurface safety valve can be reinstated as a minimum. The cut unsnarled part of the line can then be pull back out of the well.
One type of cutting tool available can be used on small diameter slickline. It is clamped around the line and dropped down the well. It relies on momentum gained during the drop to be applied as a hammer action on a cutter for cutting the line when the cutting tool impacts on the snarled tool. However a well deviation or entry of the cutter tool into liquid can slow the drop of the tool, such that the cutting tool does not have enough momentum for the hammer action to cut the line. This tool is not effective for wireline with a diameter larger than, about 7/32 inch, such as multi-strand wire or cable.
Another type of cutting tool is available which has an explosive charge on a timer. The explosive charge is used to drive a cutter to cut the line. This cutting tool is more effective than the momentum reliant one, but has its own drawbacks because of the difficulty in transportation and handling of explosives along with difficulties in obtaining approval to transport explosives, especially across international borders. Further these tools must be sent away for extended periods for redress once used.
The present invention provides a new mechanism useful in activating downhole tools, including, but not limited to, a downhole cutter tool for cutting a line.